The present invention relates to integrated circuits and other semiconductor devices and to methods for the fabrication thereof, and particularly to integrated circuits having low resistivity, high aspect ratio contacts, and methods for the fabrication thereof.
In the continuing quest for more powerful, less expensive integrated circuits, size matters. The smaller the individual circuit features, the more memory space or computing power can be packed into a given area. But circuits with very small feature sizes can be difficult to produce.
Small feature sizes cause particular problems in contact formation. Contacts are regions of electrically conductive material that provide an electrical connection (a xe2x80x9ccontactxe2x80x9d) between separate elements or portions of an integrated circuit, typically between an underlying portion of an integrated circuit and an overlying portion. As feature sizes decrease, the aspect ratio, ratio of height (or depth) to width, of such contacts generally increases. With narrower, taller contacts, the resistivity of the contact, and particularly of the junction between the contact and the circuit element or portion below it, must be kept sufficiently low. Otherwise, the electrical connection (the contact) may fail, possibly causing failure of the entire integrated circuit.
Contacts are typically formed in the following general way: A generally planar semiconductor structure has already been formed, including thereon or therein a contact area to which the contact is to be electrically connected. A layer of electrically insulating material is then formed upon the semiconductor circuit structure. A contact hole is then formed down into the insulating material above the contract area. The hole is typically formed by a patterning process, such as masking followed by a vertical anisotropic etch. The contact area at the bottom of the contract hole is then cleaned and a conductive material is deposited in the contact hole to form the contact.
For contacts with high aspect ratios, highly directional etch processes are used to form the contact holes. Such processes typically include carbon-based polymer-forming constituents in the etch plasma. After such an etch, the contact area at the bottom of the contact hole is typically contaminated or covered with residue from the etch process. The etch residue must be removed to allow the subsequently deposited conductive material to form a low resistivity contact with the contact area. A native oxide layer is also typically present on the contact area and must also be removed to allow formation of a low resistivity contact.
The semiconductor structures generally include a semiconductor substrate that is doped with a dopant such as boron or other dopants. The processing of the semiconductor structures can cause dopants to diffuse out of, or otherwise be removed from, regions or which the dopants are needed. In addition, even if the dopants remain, processing can xe2x80x9cdeactivatexe2x80x9d the dopants so that they become unavailable.
The present invention provides integrated circuits having low resistivity, high aspect ratio contacts, and methods for forming such circuits.
In one specific embodiment, contact areas comprising doped semiconductor material at the bottom of the contact holes are cleaned, in a cleaning plasma, desirably a hot hydrogen plasma. The contact holes and contact areas are also exposed in situ during and/or separately from the hot hydrogen clean to a plasma containing the same dopant species as in the doped semiconductor material forming the contact areas. Exposure to the dopant species in the plasma partially, completely, or more than completely offsets any loss of dopant due to the plasma clean, allowing good control of the dopant profile adjacent to the surface of the contact area. A protective conductive layer such as a metal silicide may then be formed over the surface of the contact area in situ, and a contact plug may also be formed thereafter over the protective layer.
The resulting integrated circuit has contacts with interfaces, such as silicide interfaces, to contact areas that have a particularly favorable dopant profile and concentration near the interfaces. For example, the dopant concentration in the contact area may be in the range of about 1018-1021 atoms per cubic centimeter somewhere within a distance of about 500 Angstroms or less from the interface with the contact. This allows reliable formation of high resolution high aspect ratio contacts (with aspect ratios as high as 8:1 or higher), having resistances which may, for example, be equal to or less than about 1000 xcexa9. Particular advantages and features of the invention will be apparent from the detailed description below.